The present invention relates to a discharge lamp having a pair of opposing discharge electrodes and enclosing mercury, rare gases, and so forth in an arc tube. It also relates to a lamp device constructed such that this kind of discharge lamp is built into the inside of a reflector. This lamp device can be used as, for example, the light source of a screen projector.
Conventionally, as, for example, the light source of a screen projector, a lamp device provided with a discharge lamp, such as a high-pressure mercury vapor discharge lamp, inside a concave reflector has been used. A discharge lamp is constructed such that a pair of opposing discharge electrodes is provided, and mercury, rare gases, and so forth are enclosed in an arc tube. In order that the interior of the arc tube be gastight, power is supplied to the discharge electrodes by means of wiring members enclosed in sealed portions, which are provided on both sides of the arc tube, and connected by welding or the like. In addition, by adjusting the discharge electrodes so as to be at a comparatively short distance from each other and forming an arc having a short arc length (short arc), projected light is efficiently supplied to a specified optical system, and thus a bright image can be projected on a screen.
A discharge lamp such as the one described above is characterized in that the arc tube reaches a very high temperature during operation. Specifically, in, for example, a 100 W to 150 W common short arc high-pressure mercury vapor discharge lamp, the maximum temperature of the arc tube (the interior wall surface side of the upper portion of the arc tube) is approximately 900xc2x0 C. to 1000xc2x0 C. In addition, the temperature of the sealed portions is about 500xc2x0 C., lower than the above-mentioned maximum temperature, but still a rather high temperature. For this reason, the wiring members disposed in the sealed portions are composed of a high melting point metal such as molybdenum. However, when the temperature of these sealed portions rises too much, the welded portions of the wiring members in the sealed portions and near the sealed portions begin to oxidize, corrode, and the like resulting in disconnection, and there is a risk of the lamp being extinguished. Thus, in a common projector, a cooling fan is provided in the main body of the projector making it possible to prevent an excessive temperature rise of the discharge lamp and the reflector. It is to be noted that, in order to prevent disconnection by oxidation and the like of the welded portions of the wiring members as described above, it is thought that the temperature of the above-mentioned welded portions should be regulated according to, for example, the standard (350xc2x0 C.) specified in the regulations for halogen lamps, xe2x80x9cTungsten Halogen Lamps,xe2x80x9d IEC (International Electrochemical Commission) 60357 and xe2x80x9cHalogen Lamps,xe2x80x9d JIS (Japanese Industrial Standards) C7527, and it is preferable to restrict the temperature to, at the highest, 400xc2x0 C. or less.
In addition, the discharge lamp is characterized in that the inside of the arc tube reaches a very high pressure during operation. Specifically, in, for example, a 100 W to 150 W common discharge lamp as above, the pressure (operating pressure) of the inside of the arc tube approaches 200 atmospheres. For this reason, when the arc tube is damaged during lamp operation, large explosive sounds and the scattering of glass fragments tend to result. The occurrence of these kinds of large explosive sounds and scattering of glass fragments, for example, especially when the discharge lamp is applied to projectors for household use, is a factor in lowering the commercial value of the lamp. Thus, lamp devices which block the open end of the reflector with a glass plate to lower the frequency of explosive sounds and the scattering of glass fragments are widely used. When a completely hermetically sealed space is formed between the reflector and the glass plate by the reflector and the glass plate, the temperature rise of the discharge lamp is considerable. On the other hand, when a notch or the like is provided in the reflector and/or the glass plate and outside air is circulated inside the lamp in order to cool the discharge lamp, in event that the arc tube is damaged, substantial reduction in explosive sounds and consistent prevention of the scattering of glass fragments and dispersal of mercury vapor are difficult to achieve.
Furthermore, in recent years, there have been increasing demands for an increase in the brightness of projected images and a reduction in the size of projectors. However, because increase in lamp power and reduction in the size of the reflector, which accompany these demands, invite an even greater temperature rise in discharge lamps, it has been difficult to satisfy the demands. Therefore, in order to sufficiently satisfy the increasing demands for an increase in the brightness of projected images and a reduction in the size of projectors, effective restriction of the temperature rise of a lamp device accompanying an increase in output and reduction in the size of a reflector and above all restriction of a temperature rise at the welded portions of wiring members are needed.
In view of the foregoing problems, it is an object of the present invention to provide a high-pressure vapor discharge lamp and a lamp device which, even with an increase in lamp power and a reduction in the size of the reflector, can prevent disconnection due to oxidation and the like of the welded portions of wiring members and the like and with which a lengthening of lamp life and a decline in the percentage of defective lamps can be expected. It is another object of the present invention to provide a lamp device that can reduce explosive sounds from the arc tube and consistently prevent the scattering of glass fragments and the dispersal of mercury vapor.
The foregoing problems are solved in one aspect of the invention, by the provision of a lamp device comprising:
a discharge lamp comprising an arc tube, the arc tube enclosing luminescent materials and having disposed therein a pair of opposing electrodes, and a pair of sealed portions extending from the arc tube (namely, the sealed portions are coupled to the arc tube);
a reflector which reflects light radiated by the discharge lamp;
a transparent member covering an open end of the reflector and accommodating the discharge lamp in a space between the transparent member and the reflector; and
means for preventing an excessive temperature rise wherein the temperature rise of welded parts of wiring members electrically connected to the electrodes is restricted.
In other words, according to the present invention, in a lamp device accommodating a discharge lamp in a space formed by a reflector and a transparent member covering the reflector, a means for preventing an excessive temperature rise of the wiring members and welded parts of the wiring members caused by the generation of heat accompanying operation of the lamp is provided. Through this means, it is possible to limit thermal degradation of the welded parts of wiring members. Thus, disconnection at the welded parts is prevented, and a lengthening of lamp life and a decline in the percentage of defective lamps can be anticipated. In addition, demands for increased lamp power and reduction in the size of reflectors can be responded to without difficulty.
The discharge lamp may have a foil sealed construction.
The present invention is useful in so-called foil sealed construction discharge lamps, which are widely used. In foil sealed construction discharge lamps, metal foils, serving as the wiring members in the sealed portions and capable of securing a large area of contact, are used such that adhesion is maintained despite the difference in the coefficients of thermal expansion of the glass and the metal foils, and the hermetic seal of the space in which the electrodes and so forth are disposed is maintained despite damage from thermal shock between the glass that forms the sealed portions and the metal foils. One end of a metal foil, located in the end portion of a sealed portion, is connected by welding to a conducting member that is connected to an external power source. By providing a means for preventing an excessive temperature rise, it is possible to prevent an excessive temperature rise at the welded parts of the metal foils and the wiring members within the sealed portions, which reach high temperatures. In addition, the temperature rise at the welded parts of wiring members which are outside the sealed portions but located near the sealed portions can be restricted.
Of course, even in lamp devices that use discharge lamps not having a foil sealed construction, for example, a discharge lamp having rod-shaped wiring members sealed in the sealed portions or a discharge lamp in which the electrodes pass through the sealed portions, disconnection at the welded parts of the rod-shaped wiring members or the electrodes and other wiring members can be prevented.
An inside space of the reflector and the transparent member may be hermetically sealed in a gastight manner. Thus, in event that the arc tube is damaged, explosive sounds can be greatly reduced and prevention of the scattering of glass fragments and the dispersal of mercury vapor can be ensured.
The pair of sealed portions may have differing lengths and the means for preventing an excessive temperature rise may be such that the longer sealed portion is on the side of the transparent member and the shorter sealed portion is on the side of the base of the reflector.
More specifically, it is preferable that an end of the sealed portion on the side of the transparent member be positioned near the transparent member.
In a lamp device, because the sealed portion on the side of the transparent member reaches a higher temperature than the sealed portion on the side of the base of the reflector, the welded parts of the wiring members in the sealed portion on the side of the transparent member are more subject to degradation by heat than are the welded parts of wiring members in the other sealed portion. In addition, in a discharge lamp having a foil sealed construction, the welded part of the metal foil and the conductive member on the side connected with an external power source is more subject to degradation by heat than is the welded part of the metal foil and the discharge electrode, which reaches a higher temperature, due to the weakness of the gastight seal. Thus, as described above, by adjusting the length of the sealed portions, because the distance from the front end of the sealed portion on the side of the transparent member to the light-emitting portion is longer than that of the other sealed portion, the temperature of the front end of the sealed portion on the side of the transparent member can be restricted to a low temperature, and disconnection by oxidation and the like of the welds of wiring members and the like in the front end of the sealed portion on the side of the transparent member or near this front end can be prevented.
The means for preventing an excessive temperature rise may be means for channeling heat such that heat from the sealed portion disposed on the side of the transparent member is conducted to the exterior of the lamp device.
For the means for channeling heat, it is possible to use, for example, a copper plate or a heat pipe having one end wrapped around the sealed portion and the other end extended to the exterior of the lamp device. By means of a heat channeling means such as this, because the heat of the sealed portion is released outside the lamp device, it is indeed possible to restrict the temperature of the front end of the sealed portion to a low temperature and to prevent disconnection by oxidation and the like of the welds of wiring members and the like.
The means for preventing an excessive temperature rise may be such that the sealed portion disposed on the side of the transparent member is integral with the transparent member
Thus, because heat from the front end of the sealed portion is released from the exterior surface of the transparent, hermetically sealed member and the like, the temperature of the front end of the sealed portion can indeed be restricted to a low temperature, and disconnection due to oxidation and the like of the welds of wiring members and the like can be prevented.
The means for preventing an excessive temperature rise may be such that the front end of the sealed portion disposed on the side of the transparent member projects into the exterior of the transparent member.
Thus, because the front end of the sealed portion is cooled by air from the outside, the temperature of the front end of the sealed portion can be restricted to a low temperature, and disconnection, due to oxidation and the like of the welds of wiring members and the like can be prevented.
A lamp device may further comprise cooling means for removing conducted heat to the exterior of the lamp device or for absorbing conducted heat.
For the cooling means, it is possible to use, for example, a cooling fan, heat releasing fins, a cooling module utilizing a Peltier element, or the like. Thus, because heat conducted by a heat channeling means, heat conducted to the surface or periphery of the transparent, hermetically sealed member, and heat from the front end of the protruding sealed portion can be efficiently released, it is possible to restrict the temperature of the front end of the sealed portion to a low temperature without difficulty.
A high-pressure vapor discharge lamp may comprise:
an arc tube enclosing luminescent materials and having disposed therein a pair of opposing electrodes; and
a pair of sealed portions extending from the arc tube, the pair of sealed portions having differing lengths.
By using a high-pressure vapor discharge lamp such as this one, it is possible to construct a lamp device which restricts the temperature of the front end of a sealed portion to a low temperature and thus can prevent disconnection due to oxidation and the like of welds of wiring members and the like.